A series of seven studies on sleep is proposed: 1. A study of behavioral and functional characteristics of a rat state characterized by low EEG, low EMG, and high theta amplitudes aims to clarify where this state belongs relative to wakefulness and sleep stages. 2. To increase our understanding of underlying oscillators, we propose to compare relationships among circadian rhythms of sleep, temperature, and activity in the rat under several light:dark schedules. 3. To understand why diurnal sleep rhythms changes with age, we propose to compare the rhythms of young and old rats under "normal" and phase reversed lighting schedules and during "free-runs". 4. To develop measures of sleep intensity, we propose to compare frequency and amplitude characteristics of the sleep EEG following sleep deprivation with baseline recordings. 5. We propose to develop improved techniques for sleep depriving animals through the use of an automated system that delivers stimuli contingent upon an animal's state. 6. To understand the large individual differences in EEG slow wave activity during sleep, we propose to examine how they are correlated with a number of physiological, psychological, and sleep parameters. 7. We propose to describe the visual characteristics of dreams by having subjects choose photographs which match the visual characteristics of their own dreams. We also propose to determine how these visual characteristics are related to phasic events during sleep.